In general, the use of optoelectronic devices as well as the desirability of tunable optoelectronic devices are known to those possessing an ordinary skill in the pertinent arts. Possible applications for tunable optoelectronic devices include, by way of non-limiting example only, optical networking applications, telecommunications applications and other wavelength selective optical applications.
Tunable devices, such as filters, often represent important optical components for optical wavelength selective applications, in particular, in optical networking and fiber optic based communications. Many other networking modules/devices may be further realized using tunable filters as fundamental building blocks.
Examples of conventional tunable filters are: an Etalon, or fabry-Perot cavity, that may be tuned by adjusting the cavity length and/or optical index of the cavity; Fiber Bragg Grating (FBG) tunable filters, that may be tuned by mechanical adjusting the fiber length through strain or stress and/or by changing an effective optical index, such as by changing the polarization of a Liquid Crystal Display (LCD) or operating temperature; and acoustic-optic tunable filters (AOTFS) that may be tuned by utilizing surface acoustic-optic effects.
An Etalon may generally be used for tunable filtering if the effective optical cavity length can be changed. Either changing the physical length of the Etalon cavity or the optical index of the cavity material may be used. A major drawback of such a tunable filter lies in the inherent trade-off between wide tuning and narrow filter bandwidth. This is due to the free spectral range (FSR) of the Etaton (Fabry-Perot) structure. Further, two high reflectivity mirrors are typically desirably required in order to achieve a narrow (high Q) filter.
In order to tune an FBG filter, the optical index of the fiber or the grating period typically needs to be tunable. Both mechanical methods, such as the application of tensile or compressive forces to the filter to change the period, and thermal methods may be used to provide such tune-ability. However, a FBG tunable filter is typically undesirably slow to respond to driving input, while the tunable range is typically undesirably small.
AOTFs generally require acoustic-optical materials as a substrate, such as for example LiNbO3. Further, AOTFs are waveguide devices, not free-space devices, often are large in size due to the acoustic-optical interaction requirements, and require high power to operate.
As set forth, such filters may form optoelectronic devices themselves, or be used in other optoelectronic devices as components. One non-limiting example of such a device which may include such a filter is an external cavity tunable laser. Drawbacks with conventional approaches may include, for example, diffraction grating based devices needing mechanical rotation of the grating angle in order to perform tuning. Such rotation may be slow in nature and costly to build. Further, super-grating and sampled/chirped grating DBR tunable lasers may require special fabrication methods. Also, tuning through carrier injection in a DBR section may require special designs. Finally, with a fixed DFB/DBR laser design, current and temperature tuning range is conventionally small.